The WTA has ranked her world No. 1 in singles on six separate occasions. She became the world No. 1 for the first time on 2002, and achieved this ranking for the sixth time on 2013. On that occasion, she held the ranking for 186 consecutive weeks, setting the joint record with Steffi Graf for the most consecutive weeks as world No. 1 by a female tennis player. In total, she has been world no. 1 for 309 weeks, which ranks her third all time among female tennis players. Williams is regarded by some commentators, players and sports writers as the greatest female tennis player of all time.

Williams holds the most major singles, doubles, and mixed doubles titles combined amongst active players, male or female. Her record of 38 major titles puts her fourth on the all-time list and second in the open era: 22 in singles, 14 in women's doubles, and two in mixed doubles.

Her total of 22 Grand Slam singles titles marks the joint record for the most Major wins by a tennis player (male or female) in the Open Era, and is tied for second on the all-time list behind Margaret Court (24), She is the only tennis player – female or male – to have won singles titles at least six times in three of the four Grand Slam tournaments. She is also the only tennis player to have won 10 Grand Slam singles titles in two separate decades. She has won an all-time record of 12 Grand Slam singles titles on hardcourt. Williams holds the Open Era record for most titles won at the Australian Open (6) and shares the Open Era record for most titles won at the US Open with Chris Evert (6). She also holds an all-time record for the most singles matches won at the Grand Slams with 309 matches.

Williams is primarily a baseline player and her game is built around taking immediate control of rallies with her powerful and consistent serve, return of serve, and forceful groundstrokes from both her forehand and backhand swings. Williams' forehand is considered to be among the most powerful shots in the women's game as is her double-handed backhand.